The prior art is aware of arrangements of controls for pumps which are used to drive various motor mechanisms or the like, such as a fluid pump used to drive a tractor transmission or mobile equipment. In those prior art arrangements, operator levers or controls are connected with the pump and maneuver the operating elements of the pump for producing the desired fluid forces, such as driving a transmission. In those arrangements, the pump develops vibrations which are transmitted back to the operator's handle or lever, and this of course is undesirable in that it is detrimental to the apparatus itself and it is also fatiguing to the operator, and thus ineffective and inefficient operations are likely to occur.
Accordingly, the prior art is aware of examples of hydrostatic drive systems, such as those which are used to drive skid-steer loaders employing variable displacement fluid pumps having a fixed displacement motor. Control of the variable displacement pumps is generally by means of linkage systems, and these systems should be arranged to provide an automatic return to a neutral position, upon the operator's release of the handle or control, and these prior art systems are usually cumbersome and necessarily complicated and involved in design and they transmit the dither or vibration through the linkage system and back to the operator's handle. The dither is high frequency and low amplitude force that is generated when the pump is operating, such as the axial piston-type pump which is employed in certain installations. The constant pounding caused by the dither effect can cause premature failure of the controls and its linkage system as well as causing operator fatigue and consequent inefficiencies.
Specific examples of prior art tractors with bucket loaders are found in U.S. Pat. Nos. 3,388,821 and 3,614,273 and 3,635,365. In those examples, the first patent shows a relatively complicated lever system for controlling valves utilized in the drive of the tractor and in the operation of the loader bucket. The second patent also shows operator controls for the fluid equipment employed; and the third patent shows operator levers which control a piston type of fluid pump which supplies fluid to a motor connected to the tractor transmission or drive mechanism. In those examples, the operator handle or lever is connected to the fluid apparatus by means of rigid types of links or the like which therefore convey the undesirable dither from the fluid apparatus to the operator's handle.
Accordingly, the present invention provides for an improvement upon the prior art arrangements and does so by avoiding the problems and undesirable features mentioned above. Specifically, the present invention provides a fluid pump control which avoids transmitting the vibrations or dither and which returns the pump to the neutral position when the operator releases the handle.
Still further, the present invention accomplishes the aforesaid objectives and it does so with control apparatus which is simple in structure but yet effective and reliable in operation and which will always create a uniform type of controlled action and will firmly and reliably return the equipment to a neutral position when the operator has released the handle.
Still further, the present invention provides the fluid control apparatus as aforesaid and it does so with equipment which is self-regulating in the amount of force or movement transmittable between the control handle and the pump or apparatus itself, but yet the apparatus is proportionately controlled and positively controlled by the handle. That is, the operator cannot force excessively on the pump or like apparatus by maneuvering the handle, and the connections between the handle and the pump give a positive type of control but limit the degree of movement therebetween and thus avoid damage to the apparatus. Therefore, the present control avoids the possibility of the operator placing excessive force on the pump itself and thus overloading the pump, such as for instance when the operator's lever or handle is moved to an extreme position. As such, the present invention has automatic compensation or limitation to avoid overloading the fluid pump or fluid apparatus.
Other objects and advantages will become apparent upon reading the following description in light of the accompanying drawings.